You can use TeamViewer or LogMeIn, both of these are free. If you have an iDevice i.e iPhone you can control either a Mac or PC via your phone, through their respective apps. I use TeamViewer daily to login into my colleagues work laptops when they get stuck with stuff.
Another route to consider is a VNC client for both machines. I also use VNC Viewer to log into my server, via VPN (more secure than your typical RDP).